UT researchers make genetic breakthroughs, unearth new facts about Aztec anthropology

Alberto Long

Based on colonial records, it was previously thought that the Otomi either left Xaltocan, or that they assimilated with the Aztecs, but new research is suggesting otherwise.

According to the research, genetics may show whether the Otomi, the original inhabitants of Xaltocan, the capital of a pre-Aztec city-state located 60 miles north of modern-day Mexico City, assimilated with the emerging Aztec empire or abandoned the city before its conquest by the Aztecs. Lisa Overholtzer, archeologist and professor of anthropology at Wichita State University in Kansas, said colonial historical records said the Otomi left Xaltocan and the Aztecs came after an Aztec ruler sent taxpayers to repopulate the state.

Following a series of excavations, Overholtzer said she noticed a remarkable continuity among the remains found at Xaltocan, roughly 60 miles north of Mexico City. She said burial sites were consistent, as were housing and trash sites. There was no gap in carbon dating that would suggest a 40-year occupation or evidence that the Otomi left in a hurry, she said. 

“So archaeologically, it didn’t look like there was much of a transition going on in terms of the population,” Overholtzer said. “That was when I contacted the DNA experts at UT-Austin.”

Overholtzer said she contacted Deborah Bolnick, a UT assistant professor of anthropology, who put one of her graduate students, Jaime Mata-Miguez, in charge of the analysis. 

After sampling mitochondrial DNA from the bodies unearthed at Xaltocan, Mata-Miguez found pre-conquest maternal DNA did not match that belonging to the post-conquest era. These results support the notion that the Aztec conquest of Xaltocan had a widespread genetic impact on the city, meaning that at least some Otomi remained in Xaltocan and intermarried with the Aztecs. 

Although the study suggests imperialism may have altered some Xaltocan households, mitochondrial DNA can only trace the population’s history along maternal lines, and more analysis will be needed to understand the causes of the genetic shift. 

“So far we have only analyzed mitochondrial DNA, which is a very small portion of our genome,” Mata-Miguez said. “So in the future, we will analyze markers in other regions of the genome, and that will give us more information, a more complete picture about Xaltocan’s population history during that period of time.”

The overall impact of the genetic shift demonstrated by the mitochondrial DNA analysis remains unclear, but suggests a more realistic story than the one told by colonial records. Ultimately, more research will have to be done to better understand the effects of Aztec imperialism on Mesoamerican populations, Overholtzer said.

“The potential for this kind of study is great, and hopefully it will inspire some other studies to be done,” Overholtzer said. “This suggests that these kinds of collaborations can be really fruitful.”